Conventionally, various capacitors have been developed in an attempt to reduce size and increase capacity. Among them, solid electrolytic capacitors are widely known as capacitors fit for size reduction. A solid electrolytic capacitor comprises an anode element, a dielectric film disposed on the anode element, and a solid electrolytic layer disposed on the dielectric film; and has an excellent feature of having a large capacity despite its small size.
Widely used as an electrolyte for the solid electrolytic layer, are a manganese oxide, a conductive polymer, etc.; and as a material for the anode element, a valve metal, examples thereof including tantalum, niobium, aluminum, and titanium. By using a valve metal as the material for the anode element, a uniform dielectric film can be formed on the surface of the anode element, by chemical conversion treatment.
Further improvements are being made on the foregoing solid electrolytic capacitor. For example, development efforts are underway for a technique to reduce particle size of particles of the metal used for the anode element which is a sintered element. By reducing the particle size of the metal particles, surface area of the anode element can be further increased, and therefore, surface area of the dielectric film can be further increased; and it is presumed that the foregoing enables larger capacity of the solid electrolytic capacitor.
For example, Patent Literatures 1 and 2 disclose a solid electrolytic capacitor having a small size and a large capacity, the capacitor comprising: an anode element which is a sintered element of titanium; and a dielectric film made of barium titanate (BaTiO3). A composite metal oxide having a perovskite structure, e.g., barium titanate, has a dielectric constant ten times or higher than that of an oxide formed by chemical conversion treatment; and it is presumed that using such a composite metal oxide enables larger capacity of the solid electrolytic capacitor.